DNA repair in human cells: from genetic complementation to isolation of genes.

The genetic disease xeroderma pigmentosum (XP) demonstrates the association between defective repair of DNA lesions and cancer. Complementation analysis performed on XP cell strains and on repair deficient rodent cell lines has revealed that at least nine and possibly more than 13 genes are involved in early steps of the excision of ultraviolet light-induced DNA lesions in mammalian cells. Two of these genes have been cloned and others are in an advanced stage of cloning. One cloned gene, ERCC-1, has been characterized at the molecular level. This human gene is homologous with excision repair genes in yeast and in Escherichia coli. These results indicate that the excision repair system is conserved during evolution. It is expected that the cloning and characterization of prokaryotic and eukaryotic repair genes will pave the way to a deeper understanding of mammalian repair systems and their association with cancer.